This invention relates to a method and device for fine granulization of sticky materials by means of controlled vortices and particularly for micronizing clays, sulphur, pigments, and the like by using controlled vortices of high velocities.
The well-known method for vortical granulization is based on the introduction of a material which has been preliminarily granulated to a given grain size and is then introduced into a tube having a wear resistant inner surface and a defined shape. The material to be milled is thrown onto the inner surface of the tube under the action of a vortex produced by an air compression system. Particles circulate within the milling tube for a time sufficient to achieve the desired level of granulation and then leave the tube for a subsequent separation operation.
The prior art devices based on the aforedescribed method include generally a circular or elliptical tube of ultrahard steel which is provided with tangential peripheral openings for feeding the material to be milled into the tube as well as with compressed gas/air feeding means which produce the vortex, and the material which has been granulated leaves the device through a central or tangential tube or tubes.
The aforedescribed method and the devices based on it have the following disadvantages: a high energy consumption due to the requirement for maintaining both a high velocity and a prolonged contact time between the material to be milled and the gaseous vortex; the unsuitablility of the devices for milling sticky materials due to their tendancy to compact the material within the milling compartment of the tube; the bulkiness and complexity of the equipment and its dependance on other auxiliary system; and finally, heating of the material as a result of its milling.